Effluent manure is an example of an animal husbandry effluent slurry on which it is desirable to perform separation and purification treatments.
Some types of manure, such as those of the porcine variety, present environmental risks. The high volume of liquid porcine manure produced in some regions coupled with its use as fertilizer in local fields, results in increased levels of phosphorus, potassium and heavy metals in the soil. This may increase the soil's susceptibility to allowing such minerals to leach into drainage waters and run-off streams. In addition, many types of manure give off disagreeable odours, which are particularly unpleasant when the manure applications are located in proximity to urban zones. There are several disposal and processing methods for manure. Flotation methods for removing solids from the liquid phase are also known in the art. Bubble injection uses injected air to bind to particles and bring them to the surface of the liquid. In particular, electroflotation employs an anode and a cathode to stimulate dissolved gas to form small bubbles to bring solids to the surface of the liquid. Electroflotation has been used in some effluent treatment processes.
Chemical treatments of manure are also used for ameliorating the separation and neutralizing unwanted or harmful compounds. Acids, bases, salts, coagulants and flocculants have been used as chemical additives in the prior art. These chemicals are often added in haphazard or non-optimal combinations to precipitate some suspended solids.
In the prior art patent and scientific literature, there are several processes that attempt to treat, purify or clarify manure or other effluent slurries to improve the solid-liquid separation by using an electrochemical procedure.
U.S. Pat. No. 6,852,226 (HIRO et al.) describes a process for the treatment of sewage waters including pre-treatment by fermentation, addition of chemical compounds such as HClO, Cl2, CaCl2 and/or Fe3+, and electroflotation.
U.S. Pat. No. 4,214,987 (CLEMENS) describes the treatment of used water from the food industry, including the addition of H2SO4 or HCl, addition of a flocculant and an electrochemical treatment by bubbles.
U.S. Pat. No. 3,975,247 (STRALSER) describes the treatment of sewage water including diluting the water to produce a solid-liquid solution in a 1:20 ratio that is flowable with the solids in suspension. This solution is macerated and sent to an electrolysis cell. Chemical compounds, such as chloride salts of Na, K, Ca or Mg may be added to the solution.
U.S. Pat. No. 4,654,071 (MIILLER) describes an electrolysis step using copper electrodes in order to treat liquid manure, preferably so as to contain few bubbles. It is described that it is preferable not to pre-treat the manure and that the manure is in the form of a slurry having a feces to urine ratio of approximately 10:1.
United States patent application published under No. 2002/0166819 (WATANABE) describes a manure treatment process including a biological treatment step followed by an electrochemical treatment. Flocculants, coagulants and salts may be added. This patent application also describes an electroflotation step.
U.S. Pat. No. 3,975,247 (STRALSER) describes the treatment of manure by the addition of coagulants/flocculants such as polymers and lime and then electro-coagulation using iron and/or aluminium electrodes.
International application published under No. WO 01/19735 (DEBILLEMONT) describes the treatment of manure by electroflotation using soluble electrodes made of Mg in order to produce the complexes MgNH4PO4. Chemicals may be added to aid the separation.
International application published under No. WO 01/85617 (TIERNY) describes a process for treating effluent containing nitrogen and phosphates, by adding a base, adjusting the pH, and then electroflotation.
The article “Electrode processes in static electrolysis of sewage from livestock farm” (DRABENT et al.), describes in its abstract the treatment of manure by dilution and then electrolysis to stimulate the coagulation of the solid particles for separation. CaO can be used in order to vary the intensity of the current in the electrolytic system.
There are a variety of processes known in the art for treating animal husbandry effluent slurries using electroflotation. The prior art of effluent slurry solid-liquid separation with electroflotation presents disadvantages related to the efficiency and effectiveness in destabilizing the colloidal liquid and in concentrating contaminants such as phosphorus in the solid phase, improving odour, reducing costs and/or improving clarity of the liquid phase. The prior art has a number of disadvantages in terms of process efficiency, scalability, robustness and/or effectiveness.
There is currently a need for an improved process for treating animal husbandry effluent slurries, such as manure, to overcome at least some of the above-mentioned disadvantages.